The tissues in the human oral cavity are generally exposed to repeated low doses of known or suspected carcinogens, such as alcohol, tobacco smoke, and x-radiation from diagnostic medical and dental radiology. The proposed study would examine the effects of concurrent, repeated exposures to low doses of x-radiation on tumor induction by repeated, low dose applications of a chemical carcinogen (DMBA), in established carcinogenic amounts, on an "in vivo" mammalian oral epithelial cell revewal system. Previous synergistic cocarcinogenesis studies of this type have been limited to relatively high radiation levels, and estimates of effects from low radiation doses have been generally arrived at through extrapolation from high dose data. Young adult male Syrian Golden hamsters will receive twice weekly topical applications of 0.1% DMBA in mineral oil on the right cheek pouch; repeated low-level radiation exposures to the head and neck on a weekly basis; or, both types of treatments concurrently. Treatments shall continue until tumors have been induced in a preponderance of the animals within a given group. The parameters of evaluation shall include the following: animal mortality; percentage tumor induction; tumor induction latent period; tumor volume and histopathology; and, tumor cytokinetic behavior. It is anticipated that the results of these experiments will provide information leading to some clarification of mechanisms involved in the interaction between concurrent exposures to low levels of x-radiation and chemical carcinogens, as well as provide a useful model system and preliminary data for more detailed quantitative studies of low-level exposures to multiple carcinogens and factors which modify host responses to these exposures. BIBLIOGRAPHIC REFERENCES: Lurie, A.G. and Casarett, G.W.: Influence of adrenalectomy on radiation hypertension and nephrosclerosis. Radiat. Res., 61:80-99, 1975. Lurie, A.G.: Applications of nuclear medicine in dentistry. In - CRC Handbook of Nuclear Medicine, Spencer, R.P. (Ed.), CRC Press, Cleveland, Ohio, 1976. (In Press).